Electronic image pickup apparatus

Abstract

An electronic image pickup apparatus comprising a zoom lens system and an image pickup device disposed on an image side of the zoom lens system and which converts an image formed by the zoom lens system into an electric signal, the zoom lens system having, in order from an object side, a negative first lens unit, a positive second lens unit, a negative third lens unit, and a positive fourth lens unit, the first lens unit having, in order from the object side, a negative lens and a reflective optical element which reflects an optical path, and during zooming from a wide-angle end to a telephoto end, each space between the lens units which are adjacent with each other being changed, the first lens unit being arranged in a fixed position to the image pickup device, and at least the second lens unit and the third lens unit being moved.

What is claimed is: 
     
       1. An electronic image pickup apparatus comprising:
 a zoom lens system; and 
 an image pickup device which is disposed on an image side of the zoom lens system and which converts an image formed by the zoom lens system into an electric signal, 
 wherein the zoom lens system comprises, in order from an object side, 
 a first lens unit having a negative refractive power, 
 a second lens unit having a positive refractive power, 
 a third lens unit having a negative refractive power, and 
 a fourth lens unit having a positive refractive power, 
 the first lens unit comprising, in order from the object side, a negative lens and a reflective optical element which reflects an optical path, 
 during zooming from a wide-angle end to a telephoto end, 
 each space between the lens units which are adjacent with each other being changed, 
 the first lens unit being arranged in a fixed position to the image pickup device, and 
 at least the second lens unit and the third lens unit being moved, 
 wherein the reflective optical element is a prism having a reflective surface, and 
 wherein said second lens unit includes a bi-convex lens element and a cemented lens component disposed on the image side of the bi-convex lens element, the cemented lens component including a positive lens element and a negative lens element, and 
 wherein the third lens unit comprises a single lens component having a negative refractive power. 
 
     
     
       2. The electronic image pickup apparatus according to  claim 1 , wherein the bi-convex lens element is a most object side lens element in the second lens unit. 
     
     
       3. The electronic image pickup apparatus according to  claim 2 , wherein the second lens unit further comprises a second bi-convex lens element. 
     
     
       4. The electronic image pickup apparatus according to  claim 1 , wherein the zoom lens system comprises an aperture stop which moves integrally with the second lens unit. 
     
     
       5. The electronic image pickup apparatus according to  claim 1 , wherein the fourth lens unit including a single lens having a positive refractive power, the total number of the lenses of the fourth lens unit being one. 
     
     
       6. The electronic image pickup apparatus according to  claim 1 , wherein the zoom lens system being constituted as a four-unit zoom lens system, the second lens unit including, in order from the object side, a plurality of positive lenses and the negative lens,
 the negative lens being cemented to the positive lens disposed on the object side of the negative lens. 
 
     
     
       7. The electronic image pickup apparatus according to  claim 1 , wherein the following condition is satisfied:
   0.4 <f 2 /ft< 0.8  (1),
 
 in which f2 is a focal length of the second lens unit, and ft is a focal length of the zoom lens system in the telephoto end. 
 
     
     
       8. The electronic image pickup apparatus according to  claim 1 , wherein the following condition is satisfied:
   1.5 <|f 1 /fw|< 3.0  (2),
 
 in which f1 is a focal length of the first lens unit, and fw is a focal length of the zoom lens system in the wide-angle end. 
 
     
     
       9. The electronic image pickup apparatus according to  claim 1 , wherein the following condition is satisfied:
   1.0 <|fL 1 /fw|< 2.0  (3),
 
 in which fL1 is a focal length fo the negative lens of the first lens unit closes to the object side, and fw is a focal length of the zoom lens system in the wide-angle end. 
 
     
     
       10. The electronic image pickup apparatus according to  claim 1 , wherein during the zooming from the wide-angle end to the telephoto end, the third lens unit moves toward the object side, and then the moves toward an image surface. 
     
     
       11. The electronic image pickup apparatus according to  claim 10 , wherein the third lens unit is arranged closer to the object side in the telephoto end than in the wide-angle end. 
     
     
       12. The electronic image pickup apparatus according to  claim 1 , wherein during the zooming from the wide-angle end to the telephoto end,
 the second lens unit moves toward the only object side, and has a state in which the second lens unit has a magnification of −1 while the second lens unit is moving, 
 the third lens unit moves toward the object side, and then moves toward an image surface, and 
 the fourth lens unit is arranged in a fixed position to the image pickup device. 
 
     
     
       13. The electronic image pickup apparatus according to  claim 1 , wherein the total number of the lenses of the third lens unit is one. 
     
     
       14. The electronic image pickup apparatus according to  claim 1 , wherein the third lens unit comprises a negative lens component which satisfies the following condition and whose concave surface faces the image side:
   1.0<( R 1 +R 2)/( R 1 −R 2)<3.0  (4),
 
 in which R1 is a paraxial radius of curvature of an object-side surface of the negative lens component, and R2 is a paraxial radius of curvature of an image-side surface of the negative lens component, the lens component being a lens having only two surfaces of the object-side surface and the image-side surface which come in contact with air in the optical path, and being a single lens or a cemented lens. 
 
     
     
       15. The electronic image pickup apparatus according to  claim 14 , wherein a lens component of the third lens unit is the only negative lens component,
 the image-side surface of the second lens unit is a concave surface, and 
 the object-side surface of the fourth lens unit is a convex surface. 
 
     
     
       16. The electronic image pickup apparatus according to  claim 1 , wherein the first lens unit includes one positive lens and one negative lens on an image-surface side of the reflective optical element. 
     
     
       17. The electronic image pickup apparatus according to  claim 1 , wherein the fourth lens unit comprises one positive lens component having an aspherical surface,
 the total number of lens components of the fourth lens unit is one, and 
 the lens component is a lens having only two surfaces of an object-side surface and an image-side surface which come in contact with air in the optical path, and is a single lens or a cemented lens. 
 
     
     
       18. The electronic image pickup apparatus according to  claim 1 , further comprising:
 a processing section which performs signal processing to electrically correct a distortion of the zoom lens system based on a signal from the image pickup device.